In Drosophila the production of red eye pigment requires the

In Drosophila, the production of red eye pigment requires the autosomal dominant allele Bn. The dominant allele Ve of an X-linked gene allows production of the brown pigment, xanthommatin, and turns the pigmented eye to purple, but its recessive allele leaves it bright red (vermillion). A fly producing no pigment has white eyes, while a VeVe;bnbn fly has brown eyes.

A. Give the expected phenotypes (and ratios) of flies of each sex in the F1 and F2 generations from a cross of true breeding brown females to true breeding vermillion males.

B. Now give the expected phenotypes (and ratios) of flies of each sex in the F1 and the F2 generations from a cross of true breeding vermillion female to true breeding brown males.

C. How are the results in B different from the results in A?

Solution

A) We get 50:50 phenotypes from crossing of true breeding brown females to true breeding vermillion males.

B) From a cross of true breeding vermillion female to true breeding brown males, we get 3:4 of the offspring to have red eyes, and 1/4 to have brown eyes.

C)The data we obtain from these crosses is based on how the brown gene is inherited. This allele appears to be inherited as a simple recessive allele.